General Data packet Radio Service (“GPRS”) is a standard for wireless communications that supports a wide range of bandwidths. The GPRS Tunneling Protocol (“GTP”) is a group of Internet Protocol (“IP”) based communications protocols used to carry GPRS within, for example, Global System for Mobile Communication (“GMS”), Universal Mobile Telecommunications System (“UMTS”) and Long Term Evolution (“LTE”) networks. GTP can be decomposed into the GTP control plane protocol (“GTP-C”) used to carry tunnel establishment signals, and the GTP user plane protocol (“GTP-U”) used to carry encapsulated data-related signals.
Current handling of GTP-U error indication messages, as described in the 3rd Generation Partnership Project (“3GPP”) standard specification, ignores dependency on other parts of the end-to-end system. This may potentially cause race conditions which trigger undesirable release procedures by the control plane protocol, such as the S1-AP control plane protocol. These procedures may have a direct impact on the subscriber's quality of experience, as the procedures cause the subscriber to temporarily lose its connectivity to the network traffic overload and unfairness conditions on the GTP-U nodes.
The 3GPP standard specification TS 29.281 describes in the User Plane section how to handle the transmission of GTP-U error indications across the S1-U interface between a Evolved Node B (“eNB”) and a Service Gateway (“SGW”). In particular, when a GTP-U node receives a GTP-U data packet carrying a user data message, i.e., a GTP protocol data unit (“G-PDU”) for which no Evolved Data packet System (“EPS”) bearer context or radio access bearer (“RAB”) exists, the GTP-U node discards the unknown G-PDU and returns a GTP error indication to the originating node. The tunnel endpoint identifier (“TEID”) from the unknown G-PDU is copied to the TEID I information element of the outgoing error indication message. Similar principles and rules apply for other GTP-U interfaces like the S5, Iu and Service GPRS Support Node (“SGSN”) to Gateway GPRS Support Node (“GGSN”) (“Gn”) interfaces.
The 3GPP standard specification TS 23.007 describes in the Restoration Procedures section how to handle the reception of GTP-U error indications at the eNB and SGW. In particular, the standards indicate that if the SGW receives a GTP error indication for a bearer context from an eNodeB for an ‘active’ mode User Equipment (“UE”), the SGW deletes all the GTP-U tunnels for this UE. The SGW further sends a downlink data notification message to the Mobility Management Entity (“MME”). If the MME receives a downlink data notification message from the SGW as a result of the SGW having received an error indication message from the eNodeB, the MME performs an S1 release procedure if the UE is in a connected state. The MME further performs a network triggered service request procedure as specified in the 3GPP standard specification TS 23.401.
If the eNodeB receives a GTP error indication from the SGW over an S1-U tunnel not doing indirect forwarding, the eNodeB initiates the Evolved Universal Terrestrial Radio Access Network RAB (“E-RAB”) release procedure and immediately locally releases the E-RAB without waiting for a response from the MME. The eNB ignores the GTP-U error indications received on X2-U interfaces or any direct forwarding tunnels between two eNBs. The same principles or rules apply to other GTP-U nodes like Packet Data Network Gateway (“PGW”) node, a Radio Network Controller (“RNC”) node, a Service GPRS Support Node (“SGSN”), and a Gateway GPRS Support Node (“GGSN”).
When the first unicast G-PDU for an unknown TEID is received, an error indication message is immediately transmitted to the GTP-U peer. Such behavior triggers the complete removal of the UE context and all associated UE bearers when one of the bearers is pre-empted (i.e., intentionally released due to radio link resource contention) on a radio node like the eNB. When a subscriber bearer is pre-empted, the bearer and associated tunnel endpoint are immediately removed by the receiving GTP-U user plane entity that is triggering the pre-emption action while the release signaling indication to inform the sending GTP-U user plane entity is in transit. If the receiving GTP-U user plane entity is actively receiving data when the bearer is pre-empted, the sending GTP-U user plane entity will receive one or more error indications before the bearer is release on its node through normal signaling procedures. This creates an undesirable race condition between the user plane error message and the control plane release message which triggers the S1 release procedure, directly impacting the quality of the subscriber experience.
For each received G-PDU for an unknown TEID, a unicast error indication message is transmitted to the GTP-U peer. The incoming volume and the receiving rate of user data messages with unknown TEIDs dictates the outgoing volume and the transmitting rate of error indication messages potentially causing overload and unfairness on the sending GTP-U user plane entity and/or the receiving GTP-U user plane entity, which wastes valuable bandwidth resources. Outgoing and incoming error indications are usually handled in the slow path and a single faulty subscriber connection may consume all of the nodal resources leaving none for the other faulty subscriber connections.
For each received error indication message, a faulty tunnel notification is sent to the GTP-U control plane entity responsible to release the subscriber connection. The incoming volume and receiving rate of error indication messages may cause overload on the GTP-U control plane entity.